/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.proxydroid.utils;

import java.io.Serializable;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * <b>Regular Expression</b> validation (using JDK 1.4+ regex support).
 * <p>
 * Construct the validator either for a single regular expression or a set
 * (array) of regular expressions. By default validation is <i>case
 * sensitive</i> but constructors are provided to allow <i>case in-sensitive</i>
 * validation. For example to create a validator which does <i>case
 * in-sensitive</i> validation for a set of regular expressions:
 * 
 * <pre>
 *         String[] regexs = new String[] {...};
 *         RegexValidator validator = new RegexValidator(regexs, false);
 * </pre>
 * <p>
 * <ul>
 * <li>Validate <code>true</code> or <code>false</code>:</li>
 * <ul>
 * <li><code>boolean valid = validator.isValid(value);</code></li>
 * </ul>
 * <li>Validate returning an aggregated String of the matched groups:</li>
 * <ul>
 * <li><code>String result = validator.validate(value);</code></li>
 * </ul>
 * <li>Validate returning the matched groups:</li>
 * <ul>
 * <li><code>String[] result = validator.match(value);</code></li>
 * </ul>
 * </ul>
 * <p>
 * Cached instances pre-compile and re-use {@link Pattern}(s) - which according
 * to the {@link Pattern} API are safe to use in a multi-threaded environment.
 * 
 * @version $Revision$ $Date$
 * @since Validator 1.4
 */
public class RegexValidator implements Serializable {

	private final Pattern[] patterns;

	/**
	 * Construct a <i>case sensitive</i> validator for a single regular
	 * expression.
	 * 
	 * @param regex
	 *            The regular expression this validator will validate against
	 */
	public RegexValidator(String regex) {
		this(regex, true);
	}

	/**
	 * Construct a validator for a single regular expression with the specified
	 * case sensitivity.
	 * 
	 * @param regex
	 *            The regular expression this validator will validate against
	 * @param caseSensitive
	 *            when <code>true</code> matching is <i>case sensitive</i>,
	 *            otherwise matching is <i>case in-sensitive</i>
	 */
	public RegexValidator(String regex, boolean caseSensitive) {
		this(new String[] { regex }, caseSensitive);
	}

	/**
	 * Construct a <i>case sensitive</i> validator that matches any one of the
	 * set of regular expressions.
	 * 
	 * @param regexs
	 *            The set of regular expressions this validator will validate
	 *            against
	 */
	public RegexValidator(String[] regexs) {
		this(regexs, true);
	}

	/**
	 * Construct a validator that matches any one of the set of regular
	 * expressions with the specified case sensitivity.
	 * 
	 * @param regexs
	 *            The set of regular expressions this validator will validate
	 *            against
	 * @param caseSensitive
	 *            when <code>true</code> matching is <i>case sensitive</i>,
	 *            otherwise matching is <i>case in-sensitive</i>
	 */
	public RegexValidator(String[] regexs, boolean caseSensitive) {
		if (regexs == null || regexs.length == 0) {
			throw new IllegalArgumentException(
					"Regular expressions are missing");
		}
		patterns = new Pattern[regexs.length];
		int flags = (caseSensitive ? 0 : Pattern.CASE_INSENSITIVE);
		for (int i = 0; i < regexs.length; i++) {
			if (regexs[i] == null || regexs[i].length() == 0) {
				throw new IllegalArgumentException("Regular expression[" + i
						+ "] is missing");
			}
			patterns[i] = Pattern.compile(regexs[i], flags);
		}
	}

	/**
	 * Validate a value against the set of regular expressions.
	 * 
	 * @param value
	 *            The value to validate.
	 * @return <code>true</code> if the value is valid otherwise
	 *         <code>false</code>.
	 */
	public boolean isValid(String value) {
		if (value == null) {
			return false;
		}
		for (int i = 0; i < patterns.length; i++) {
			if (patterns[i].matcher(value).matches()) {
				return true;
			}
		}
		return false;
	}

	/**
	 * Validate a value against the set of regular expressions returning the
	 * array of matched groups.
	 * 
	 * @param value
	 *            The value to validate.
	 * @return String array of the <i>groups</i> matched if valid or
	 *         <code>null</code> if invalid
	 */
	public String[] match(String value) {
		if (value == null) {
			return null;
		}
		for (int i = 0; i < patterns.length; i++) {
			Matcher matcher = patterns[i].matcher(value);
			if (matcher.matches()) {
				int count = matcher.groupCount();
				String[] groups = new String[count];
				for (int j = 0; j < count; j++) {
					groups[j] = matcher.group(j + 1);
				}
				return groups;
			}
		}
		return null;
	}

	/**
	 * Validate a value against the set of regular expressions returning a
	 * String value of the aggregated groups.
	 * 
	 * @param value
	 *            The value to validate.
	 * @return Aggregated String value comprised of the <i>groups</i> matched if
	 *         valid or <code>null</code> if invalid
	 */
	public String validate(String value) {
		if (value == null) {
			return null;
		}
		for (int i = 0; i < patterns.length; i++) {
			Matcher matcher = patterns[i].matcher(value);
			if (matcher.matches()) {
				int count = matcher.groupCount();
				if (count == 1) {
					return matcher.group(1);
				}
				StringBuffer buffer = new StringBuffer();
				for (int j = 0; j < count; j++) {
					String component = matcher.group(j + 1);
					if (component != null) {
						buffer.append(component);
					}
				}
				return buffer.toString();
			}
		}
		return null;
	}

	/**
	 * Provide a String representation of this validator.
	 * 
	 * @return A String representation of this validator
	 */
	@Override
	public String toString() {
		StringBuffer buffer = new StringBuffer();
		buffer.append("RegexValidator{");
		for (int i = 0; i < patterns.length; i++) {
			if (i > 0) {
				buffer.append(",");
			}
			buffer.append(patterns[i].pattern());
		}
		buffer.append("}");
		return buffer.toString();
	}

}